At present, many communication systems are provided not only with a conventional switching function, but also with a local switching function, when meeting a certain condition, the communication system can switch between the two modes above.
Conventional switching, as shown in FIG. 1, refers to a mode in which the switch between a calling Base Station (BS) and a called BS needs to be performed through a core network. In this mode, a Base Station Controller (BSC) allocates and activates, through a control plane, a Real Time Transport Protocol (RTP) link required by a user plane to perform communicating; during this period, the quality statistic information of the RTP link is sent to the BSC through a Realtime Transport Control Protocol (RTCP) link which has a different port but the same Internet Protocol (IP) address with the RTP link; that is, in the conventional switching mode, when a person gets through, the control plane voice and the user plane voice both flow through the BSC and the core network. The RTCP link and the RTP link are in a one-to-one correspondence relationship, i.e., one RTCP link corresponds to one RTP link, and the corresponding quality statistic information of the RTP link is transmitted to the BSC. The RTCP link and the RTP link have different ports but the same IP address. The RTCP link will be informed of the quality statistic information of the RTP link at regular time intervals, and then reports the quality statistic information to the BSC. According to the received link quality statistic information, the BSC learns the user plane link situation and processes it in time, and at the same reports the RTP link situation.
At this moment, on the control plane, the BS reports the measurement result message to the BSC periodically, the message mainly includes the quality and the level of the radio link.
FIG. 2 shows a message flowchart illustrating that a call enters into a local switching mode from a conventional switching mode in the prior art, comprising the following steps:
step 201: in the conventional switching mode, the RTP link has been established and the call is underway;
step 202: the BSC decides to enter into the local switching mode;
step 203: the BSC transmits new-channel establishment messages to a BS 1 and a BS 2 respectively to notify the BS to establish a new RTP link;
wherein, the new-channel establishment message sent to the BS 1 contains a local switching identifier, the IP address and the port number of the BS 2; the new-channel establishment message sent to the BS 2 contains a local switching identifier, the IP address and the port number of the BS 1; the local switching identifier is used for indicating that the purpose of establishing a new channel this time is to perform local switching;
step 204: after obtaining from the new-channel establishment messages the information of establishing new RTP links, the BS 1 and the BS 2 perform RTP link establishment and record the switching mode identifier as local switching;
step 205: the BS 1 and the BS 2 report RTP establishment success messages to the BSC;
step 206: after guaranteeing the intercommunication of the RTP links of the BS 1 and the BS 2, the BSC transmits an old-channel (that is, the RTP link originally used) release message to the BS 1 and the BS 2;
step 207: after receiving the old-channel release message, the BS 1 and the BS 2 release channels, and report releasing complete messages to the BSC after completing the release;
step 208: the BS 1 and the BS 2 record the switching complete identifier as ‘completed’;
step 209: the current call is performed in the local switching mode.
FIG. 3 shows a message flowchart illustrating that a call enters into a conventional switching model from a local switching mode in the prior art, comprising the following steps:
step 301: in the local switching mode, the RTP link has been established and the call is underway;
step 302: the BSC decides to enter into the conventional switching mode;
step 303: the BSC transmits new-channel establishment messages to a BS 1 and a BS 2 respectively to notify the BS to establish a new RTP link;
wherein, the new-channel establishment message sent to the BS 1 contains a conventional switching identifier, the IP address and the port number of the BSC; the new-channel establishment message sent to the BS 2 contains a conventional switching identifier, the IP address and the port number of the BSC; the conventional switching identifier is used for indicating that the purpose of establishing a new channel this time is to perform a conventional switching;
step 304: after obtaining from the new-channel establishment messages the information of establishing new RTP links, the BS 1 and the BS 2 perform RTP link establishment and record the switching mode identifier as a conventional switching;
step 305: the BS 1 and the BS 2 report RTP establishment success messages to the BSC;
step 306: after guaranteeing the intercommunication of the RTP links of the BS 1 and the BS 2, the BSC transmits an old-channel (that is, the RTP link originally used) release message to the BS 1 and the BS 2;
step 307: after receiving the old-channel release message, the BS 1 and the BS 2 release channels, and report Releasing complete messages to the BSC after completing the release;
step 308: the BS 1 and the BS 2 record the switching complete identifier as ‘completed’;
step 309: the current call is performed in the conventional switching mode.
Local switching, as shown in FIG. 4, refers to a mode in which the call between a calling user and a called user no longer passes through the core network and is directly performed between the calling BS and the called BS when the calling user and the called user satisfy certain conditions. The advantages of this mode are as follows: the occupation of the core network resource is reduced, the transmission delay of the voice is shortened, the utilized bandwidth of the Abis interface and the like is reduced and convenience is brought to the operator and the user. The most important characteristic of the local switching is that: in the local switching mode, the control plane flow keeps unchanged during the call; however, the user plane data is no longer transmitted through the core network and is directly transmitted between the BSs. As shown in FIG. 2, in this mode, the RTP link on which the voice is transported has been re-established between the BSs, the original RTP link between the BS and the BSC has been removed; therefore, the link quality statistic information which is transmitted through the RTCP link is sent to the opposite BS accordingly; on one hand, the opposite BS does not have to and cannot process the received information; on the other hand, the BSC which needs the information cannot receive the information since the link between the BS and the BSC is released. Therefore, it has become an important problem on how to transmit the quality statistic information of the call link to the BSC in the local switching mode such that the BSC and the staff can prevent the out-of-control of the user plane.